Chiron and the centaurs return Percy, Annabeth, and the others to Camp Half-Blood just after Clarisse. The camp shows signs of the recent attacks, with burned buildings and many wounded campers, but the mood changes when Clarisse hangs the Golden Fleece on Thalia's tree. Under the moonlight, the tree begins to recover as its needles turn green again, proving the poison is being driven out. Chiron orders the Fleece guarded, and Clarisse is publicly honored while Percy and Annabeth quietly blend back into camp life.

The next day, Chiron announces that the chariot races will still be held. Percy teams up with Annabeth while Tyson repairs Athena's chariot and adds powerful new features. Percy wants to win more than he cares about the prize, and the team spends two days preparing.

The night before the race, Hermes visits Percy in the stables. Percy apologizes for failing to bring Luke back, but Hermes explains that gods often have to help their children indirectly and suggests that Poseidon has been watching over Percy more than Percy realizes. Hermes then delivers a letter from Poseidon. Percy hopes for praise or answers, but the note contains only two words: Brace Yourself, which leaves Percy unsettled and anxious.

On race day, Percy is distracted by the warning until Tyson gives him a watch he has built and finally explains his feelings. Tyson says he once prayed to Poseidon for a friend after a lonely and dangerous childhood, and Percy was the answer to that prayer. The conversation helps Percy understand Tyson's loyalty and Poseidon's role in bringing them together. Percy enters the race with Annabeth, using Tyson's improved chariot and special weapons to gain an early lead.

The race turns dangerous when Apollo damages Athena's wheel and Hephaestus closes in. Beckendorf's team snares their chariot and then throws Greek fire aboard, forcing Percy to react quickly. Percy activates Tyson's watch, which transforms into a shield, uses it to beat back Beckendorf, and flips the Greek fire into the Hephaestus chariot, causing it to explode and clear the way. Annabeth drives them across the finish line, and when the crowd celebrates, Percy publicly calls Tyson his brother. Annabeth backs him up, gives Percy a kiss on the cheek, and the three of them share the victory together.